There has long existed a need for a low-cost, dependable way to ascertain the presence and depth of fish or other bait-taking aquatic creatures. A major problem which commercial fishing fleets constantly confront is the inability to locate schools of fish. Water temperature and currents may be measured and analyzed in order to provide possible indications of areas of the sea in which a school of fish might be found, but the process of locating migratory schools of fish has always involved a great deal of quess-work and intuition. Since little is known about the migration patterns of schools of fish, a fishing captain's "Sixth Sense" as to where fish can be found is often far more reliable than presently-existing scientific analysis.
An alternate and more reliable way to locate schools of fish is to actually sense their presence. Sonar or radar is often used to detect the presence of a large school of fish. It is typically impractical to deploy large numbers of such detecting devices because of the large expense involved and the short life span of the devices due to the harshness of the sea environment. Sensing systems are sometimes placed aboard helicopters or other aircraft which fly over the surface of the sea in search of schools of fish. However, sonar or radar systems are relatively expensive to obtain and operate and often require a skilled individual to operate the controls and analyze the data provided.